To develop the traction or clamping force required at the belt/sheave interface of a continuously variable transmission (CVT), a pump is conventionally used to generate hydraulic pressure which biases a movable sheave member toward an opposed sheave member. Another recognized method of developing the clamping force is through the use of a cooperating ball and camming surface arrangement. In U.S. Pat. No. 2,651,208 to Karig, for instance, the torque from an input shaft forces various balls against angularly arranged cam surfaces provided on a movable pulley sheave to thereby produce an axial force component on the sheave. U.S. Pat. No. 4,116,080 to Berens discloses an infinitely variable transmission in which rolling elements subject to centrifugal force bear against an inclined abutment surface and generate an axial force component to assist in the clamping force of pulley sheaves.
It is also known to use the radial displacement of a weight against an inclined surface to generate the axial clamping force. This radial displacement occurs when the shafts upon which the sheaves are mounted rotate. For example, U.S. Pat. No. 4,360,353 to Hattori et al discloses a torque transmission system in which flyweights in a driven pulley unit are radially displaced by centrifugal force. The driven pulley unit is axially shifted by the axial force component of the flyweights bearing against inclined surfaces. Similarly, U.S. Pat. No. 4,487,595 to Quick et al discloses a pulley construction for a V-belt having a speed responsive unit for moving a flange axially relative to another flange. As the speed of rotation of the pulley construction increases, steel balls are thrown outwardly by a greater centrifugal force. The balls move outward in tracks to cause a pulley flange to be axially moved toward an opposite pulley flange. Also, U.S Pat. No. 4,515,575 to Kinbara et al discloses a torque transmission system in which the movable pulley part of the driven pulley unit is axially shifted by the action of flyweights. When the flyweights are centrifugally moved toward their radially outermost positions, an axial thrust force is imparted to the movable pulley part by the flyweight bearing against inclined surfaces.
A problem with the displacement of weights, however, is that the weights may quickly shift position upon application or reversal of torque. The consequent impact of the weights with their retaining surfaces results in backlash which can damage the CVT.